In recent years, commercial use projector apparatuses, in particular, become larger and heavier, following the trend of projecting larger images and enhancing the quality thereof. Such large and heavy projector apparatus cannot usually be easily moved once installed.
With such background, Japanese Patent Laid-open Publication No. Hei 9-138377, for example, discloses a structure capable of changing a relative distance between the central line of the luminous flux of image light and the optical axis of the lens unit so that an image can be projected onto a desired position on the screen from the projector apparatus with a main body thereof fixedly installed. This structure can slide the position on the screen, onto which the image light is projected from the projector apparatus.
According to such a projector apparatus, when the central line of the incident light coincides with the optical axis of the lens unit, that is, the distance between the central line and the optical axis is zero, the luminous flux of image light and the optical axis of the lens are perpendicular to the screen. With the above, an image as initially desired is shown, giving no sense of discomfort to the viewer. Thus no problems at all are caused.
However, when the central line of the incident light does not coincide with the optical axis of the lens unit, producing a relative distance therebetween, an angle results between the optical axis of the lens unit and the optical axis of the projected light from the lens unit towards the screen. In the above, the optical axis of the projected light forms an angle relative to the direction perpendicular to the screen. That is, the projected light reaches the screen with the optical axis thereof diagonal to the direction perpendicular to the screen. This results in an image that is different from the one initially desired being shown on the screen. Specifically, as shown in FIG. 12, the angle of view is distorted; the overall brightness is inconsistent; and blur expands due to the focus not being properly adjusted. The larger the relative distance between the central line of the incident light and the optical axis of the lens unit becomes, in other words, the larger the distance between the point where the optical axis of the lens unit contacts with the wall on which the screen provided thereon and the image actually shown on the screen becomes, the more serious the above-described problem of distortion and/or blur becomes. Consequently, only a part of the light from the condenser is directed to the lens unit, and an image with parts missing thus results.
Here, when the slide amount of the image on the screen is small, the distortion and blur of the image may be practically tolerable. However, with the image sliding excessively, the viewer of the image may recognize obvious distortion and/or blur of the image, which could be a practical problem.
As described above, the above-described projector apparatus has a possibility that positional adjustment of an image on the screen may result in distortion and blur of the image, which are large enough to cause a practical problem. The present invention aims to address this deficiency.